1. Field of the Invention
The present invention relates to a measurement system for characterizing power amplifier performance and, more particularly, for providing an automated testing and measurement system for tuning in real time a radio frequency amplifier after the device and matching circuits have been assembled.
2. Description of the Prior Art
It is always desirous to obtain measurements which can improve the development of solid-state power amplifiers because of the large volume of measurements involved in such a development. The measurements are needed to characterize the devices used in an amplifier, so that matching circuits can be designed, and to tune the amplifier after the device and matching circuits have been assembled. Empirical tuning is required because of variations in device parameters, variations in matching network performance due to fabrication tolerances, and limitations in the data obtained in the initial device characterization.
An example of a prior art testing and measurement system is disclosed in the article "Fabrication of Lumped-Element Broadband GaAs MESFET Microwave Power Amplifiers" by J. B. Klatskin et al in RCA Review, Vol. 42, No. 4, December 1981, at pages 576-595. There, at page 591, it is described that computer analysis permits complete optimization of an amplifier at the point of manufacture. More particularly, the completed amplifier S-parameters are measured and the measured capacitance and inductance are compared to the design values using either the standard FET data or the original S-parameter data of the device. From this information, a decision is made to either (a) replace the device, (b) print a parallel wire if the required inductance is in an adjustable range, or (c) connect tuning pads when the capacitance has too low a value. The amplifier is remeasured after any changes until it is no longer feasible to implement changes.
A circuit for testing the high frequency current amplifying capability of bipolar transistors is disclosed in U.S. Pat. No. 4,135,153 issued to D. C. Stone on Jan. 16, 1979. There, a transistor test circuit provides for the selection of preferably three widely differing test frequencies for testing transistors normally having respectively relatively small, intermediate and large frequency gain-bandwidth product characteristics. The test circuit is designed to form a linear amplifier circuit with a transistor under test and is provided with an automatic base drive control circuit which provides a substantially fixed predetermined DC collector current. The circuit further includes an indicating means for displaying the product of the selected tests frequency and the current gain of the transistor under test.
The problem remaining in the prior art is to provide a test and measurement system for radio frequency power amplifiers which provides fast, accurate amplifier performance data can improve empirical optimization, allow experimentation over a wide range of tuning parameters, and provide more information on the relationships between parameters.